The eye structure

• The vitreous humor fills the space between the lens and retina, providing support and maintaining the shape of the eyeball.
• The ciliary muscle controls the shape of the lens, allowing it to focus on near or far objects.
• The lens is located behind the iris.
• The sclera is the white part of the eye and provides structural support to the entire globe.
• The cornea is the clear front surface of the eye that allows light to enter and focus on the retina.
• The pupil is the black circle in the center of the eye that regulates the amount of light entering the eye.
• The optic nerve carries impulses from the retina to the brain.
• Define accommodation

  the process of changing the shape of the lens to focus on near or distant objects
• when we look at an object close up, the ciliary muscle contracts which relaxes the suspensory ligament allowing the lens to become more curved so it can refract light rays onto the retina
• When we look at something far away, the ciliary muscles are relaxed and the suspensory ligaments pull the lens into its natural position (concave)
• When light meets the eye what is the first structure it meets?


  The cornea
• What feature does the cornea have?

  It is completely transparent to allow all the light to pass through —> so has no blood vessels
• Why is the fact that the cornea has no blood vessels significant in giving it oxygen?

  Oxygen has to be diffused in from the surroundings rather than in the blood
• Why do we need the cornea?

  Causes light entering the eye to be refracted
• What is the iris?

  The coloured part of the eye.
• What does the iris do?

  Controls the size of the pupil
• What is the pupil?

  Opening in the middle of the iris that allows light to pass through to the lens
• What is the purpose of the lens?

  To refract light
• What feature can the lens perform?

  Changing the shape to change how small or large the angle of refraction is to always allow light to focus on the retina
• Where is the retina located?

  On the back of the eye
• What is the fovea?

  > The central part of the retina where light from the lens is refracted to

  > Only made up of cone cells (detect the colour of light
• What are the 2 receptor cells that the retina is made up of?

  > Cone cells:

  • Sensitive to the colour of light
  • But don’t work well in low light conditions

  > Rod cells:

  • More sensitive to light
  • Only allow us to see in black and white
• Why can you not see colour in the dark?

  Only the rod cells in the retina that are working which only allow us to see in black and white
• What is the optic nerve?

  Transmits impulses generated by receptor cells in retina to the brain
• What is it called when the eye is in low light?

  Dilated
• What is it called when the eye is in bright light?

  Constricted
• Why is the pupil made smaller in bright light?

  > Bright light in high concentrations can damage the retina

  > So make pupil smaller to lower the concentration of light being recepted
• Why is the pupil larger in low levels of light?

  > Allows more light in

  > Able to see in the dark
• What muscles are the iris made up of to control constriction and dilation?

  Circular muscle (inside of iris) and radial muscles (outside of iris)
• What happens to the muscles in the iris when constriction (make pupil smaller) needs to happen?

  Circular muscles contract and radial muscles relaxed to be stretched longer
• What happens to the muscles in the iris when dilation (making pupil larger) needs to happen?

  Circular muscles relax and radial muscles contract
• What do the ciliary muscles and suspensory ligaments do?

  Control the shape of the lens
• How much does the cornea refract light by?

  The same amount all the time
• What is the role of the lens?

  To fine tune the angle of refraction so that the light rays always meets the fovea
• What happens to the light rays from an object being recepted from close range?

  Large refraction must happens in the lens
• Why Is there less refraction in an object far away?

  Light rays are almost parallel with fovea
• To refract more strongly what must be the shape of the lens?

  Short and fat (convex)
• What is a concave structur?

  Less rounded
• What is a convex structure?

  More curved
• What happens when viewing an object close up?

  Ciliary muscles contract allowing the suspensory ligaments to loosen which means they are no longer pulling tightly on the lens so it can return to its natural wider and rounder shape to refract light more strongly